1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing system. More specifically, the present invention relates to a substrate processing method and a substrate processing system for processing a substrate provided with a resist film and a protective film overlying the resist film by an immersion exposure process that forms an immersion liquid layer on the protective film.
2. Description of the Related Art
A photoresist pattern forming process, namely, one of processes for fabricating a semiconductor device, coats a surface of a semiconductor wafer (hereinafter, referred to simply as “wafer”) with a resist film, exposes the resist film through a mask provided with a predetermined pattern, and develops the exposed resist film to form a resist pattern.
Recently, progressive miniaturization of device patterns and progressive thickness reduction of film require further improvement of exposure resolution. An immersion exposure method is one of methods intended to increase resolution by improving exposure techniques using an existing light source, such as an argon fluoride (ArF) light source or a krypton fluoride (KrF) light source. The immersion exposure method subjects a wafer to an exposure process after forming a transparent immersion liquid layer on a surface of the wafer. The immersion exposure technique passes light through, for example, pure water to utilize the effect of pure water to shorten the wavelength of light. The wavelength of light emitted by an ArF light source shortens from 198 nm to 134 nm in water. immersion liquid layer (liquid film) between a lens and a surface of a wafer, projects light by a light source through the liquid film on the wafer to transfer a predetermined resist pattern (circuit pattern) on a resist film formed on the wafer. In this state, where the liquid film is formed on the wafer, the exposure device is slid horizontally relative to the wafer to dispose the exposure device at a position corresponding to the next transfer area (shot area), and then projects light on the wafer. This procedure is repeated to transfer the circuit pattern in order to shot areas on the surface of the wafer.
Since the immersion exposure technique forms the liquid film (immersion liquid layer) in a space between a lens and a surface of a wafer, a very small amount of part of the components of the resist dissolves into the liquid film. Eluted components adhere to the surface of the lens to deteriorate the accuracy of the line width of the circuit pattern transferred to the wafer. Even if the eluted components do not adhere to the surface of the lens, an eluate contained in the liquid film affects the refractive index of the liquid film. Consequently, the resolution is deteriorated and the intrasurface accuracy of line width becomes irregular.
A method proposed in JP-A 2006-80404 (Claims, Paragraphs 0009, 0015, 0017, and FIG. 10) to solve the foregoing problems coats the resist film with an antireflection film (protective film).
The surface of the protective film is not necessarily uniformly flat and, in some cases, surface defects, such as depressions, are formed in the surface. The problem attributable to the dissolution of the components of the resist film does not arise when the surface does not have many surface defects. However, it is possible that the components of the resist film dissolves through the surface defects in the immersion liquid layer during the immersion exposure process, the dissolved components adhere to the lens and, consequently, the accuracy of line width of the circuit pattern is reduced and the accuracy of line width becomes possible when the surface has many surface defects.